In a protective circuit and device for protecting an insulator for a gate of the MOSFET to be protected from destruction, it has been required for the circuit and device to have characteristics that it operates as a large resistance for an excessive input and as a small resistance for a signal input.
Although there is a generally known protective circuit wherein the breakdown characteristic of a diode is utilized, this circuit cannot satisfy the requirement since a resistor in series with the gate of the MOSFET to be protected should be utilized.
There has been proposed a protective circuit which satisfies the requirement, wherein a depletion-type MOSFET the source of which is connected to the gate of the MOSFET to be protected and the gate of which is grounded is utilized. This circuit, however, has such drawbacks that the integration of a device corresponding to this circuit becomes difficult since the gate should be grounded, circuit design becomes complex, and the gate insulator of the protecting MOSFET may be destroyed by an excessive input.